Hypertext mark-up language (HTML) is a presentation mark-up language for displaying interactive data in a web browser. However, HTML is a rigidly-defined language and cannot support all enterprise data types. As a result of such shortcomings, HTML provided the impetus to create the extensible mark-up language (XML). The XML standard allows an enterprise to define its mark-up languages with emphasis on specific tasks, such as electronic commerce, supply chain integration, data management and publishing.
XML, a subset of the standard generalized mark-up language (SGML), is the universal format for data on the worldwide web. Using XML, users can create customized tags, enabling the definition, transmission, validation and interpretation of data between applications and between individuals or groups of individuals. XML is a complementary format to HTML and is similar to HTML as both contain mark-up symbols to describe the contents of a page or file. A difference, however, is that HTML is primarily designed to specify the interaction and display text and graphic images of a web page. XML does not have a specific application and can be designed for a wide variety of applications.
For these reasons, XML is rapidly becoming the strategic instrument for defining corporate data across a number of application domains. The properties of XML mark-up make it suitable for representing data, concepts and context in an open, vender and language neutral manner. XML uses tags, such as, for example, identifiers that signal the start and end of a related block of data, to recreate a hierarchy of related data components called elements. In turn, this hierarchy of elements provides context (implied meaning based on location) and encapsulation. As a result, there is a greater opportunity to reuse this data outside the application and data sources from which it was derived.
SAX (simple application programming interface (API)) for XML, is a traditional, event-driven parser. SAX reads the XML document incrementally, calling certain call-back functions in the application code whenever it recognizes a token. Call-back events are generated for the beginning and end of a document, the beginning and end of an element, etc. The SAX parser may populate an event queue with detected SAX events to enable certain call-back functions in the user application code whenever a recognized token is detected.